Improved acidolytic deprotection conditions for the Fmoc-based solid-phasesynthesis of thioxo peptides

The acid-mediated cleavage of a synthetic thioxo peptide was monitored usin g deprotection cocktails with varying concentrations of TFA. Thioxo peptide s are acid labile, undergoing cleavage at the amide linkage immediately fol lowing the thioamide linkage in the sequence, This acid lability makes Fmoc -based synthesis the method of choice for thioxo peptide preparation. The e xtent of cleavage increases with increased TFA concentration and longer rea ction time. Data presented herein indicate that deprotection protocols invo lving low TFA concentration (ca. 80%) and short reaction times (ca. 2 h) mi nimize the losses due to acidolytic cleavage. (C) 2001 Elsevier Science Ltd . All rights reserved.